Just scroll down to the bottom of the page and you'll see a box under the heading "Quick Reply". Simply type your message in that box and post it by clicking the button beneath which says "Post Quick Reply".

Select "Post Reply" (not, "Quick Reply) and then scroll down to the "additional options" menu and select "manage attachments." Which will open up another dialogue box where you will have to "browse" your computer to find and locate your picture, link to it, the click on the "upload" button, and then "submit reply" - and your picture will appear in your reply.